What’s Up With the Male Dolphins of Shark Bay Who Don’t Use Sponges?

As discussed in detail in a recent AnimalWise post, a group of female bottlenose dolphins in Shark Bay, Western Australia has enjoyed quite a bit of attention of late for creatively using marine basket sponges as tools to assist them in rooting out bottom-dwelling fish. While the spotlight has been on the females, not much has been said about the males who (despite growing up fin-to-fin with sisters who learn how to use sponges) generally do not become spongers. The researchers studying the sponging behavior have not explored the lack of male sponging in depth, but have hypothesized that the males may be too focused on establishing and maintaining “alliances” to be able to devote the time and effort necessary to become specialized sponge-using foragers.1

I can't figure out that sponging thing either... (photo credit: Shark Bay Dolphin Project)

So what are these male alliances all about, and why are they so important?

Fortunately, a study published in the August 23, 2011 issue of Biology Letters2 provides some new detail and insight into male bottlenose dolphin alliances in Shark Bay.

In a surprise to most likely no one, the alliances are all about sex – maximizing a male’s chances of being able to mate. What is surprising, however, is the level of complexity of these male relationships.

Only humans and Shark Bay bottlenose dolphins are known to have multiple-level male alliances within a social network.

The researchers already knew that the Shark Bay males formed two distinct levels of alliance: first-order groupings of three (or, less frequently, two) males who cooperate to establish and maintain “consortships” with females, and second-order alliances comprised of two or more primary groups who band together to take females from other alliances and/or to defend against such “theft” attempts.

In itself, this degree of cooperation is notable, as alliances and coalitions within social groups are considered to be a hallmark of social complexity (for a posting on female elephant social networks, see here, and for hyena social dynamics, see here). The researchers put it succinctly: “Only humans and Shark Bay bottlenose dolphins are known to have multiple-level male alliances within a social network.” (AnimalWise aside: why are males less apt to have multi-tier social networks than females? Ok, perhaps I don’t need to ask….)

Are you in my second-order alliance? This is all so complicated! (photo credit: Shark Bay Dolphin Project)

In this most recent study, the research team describes a Shark Bay male dolphin society that is even more complex than previously reported – one that actually has three levels of nested alliances among males.

The researchers spent over five years observing 121 frequently-seen males in over 500 consortships, concluding that amicable low-level associations (i.e., third-order alliances) were regularly occurring between specific second-order alliances and trios or other second-order alliances. The researchers further noted that fights involving multiple groups of males suggested that the third-order alliances, like the second-order ones, are employed in conflicts over females, as higher-order alliances could be useful if second-order partners were not around when rivals appeared.

A few other interesting research findings include:

  • There was a nearly continuous range in the size of second-order alliances, which had between six and 14 members.
  • There did not appear to be a relationship between the size of the second-order alliances and how stable (long-lasting) their component first-order trios were.
  • Most of the males participated in second-order alliances, but a subset of five trios did not. Of these five trios, four were comprised of older males whose prior second-order alliance partners had disappeared over time. The researchers surmised that these particular dolphins may have participated in third-order alliances because they were particularly in need of assistance in protecting and obtaining females.
  • Most of the first-order trios associated with only one second-order alliance, but a small subset (around 3%) associated with more than one second-order alliance.

So, to sum up, while (a subset of about 1/11 of) the female bottlenoses of Shark Bay are engaging in specialized tool use with marine sponges, the males are absorbed in complex Machiavellian political relationships and sexual maneuvering. Hmm, sounds a bit familiar.

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1Mann, J., Sargeant, B., Watson-Capps, J., Gibson, Q., Heithaus, M., Connor, R., & Patterson, E. (2008). Why Do Dolphins Carry Sponges? PLoS ONE, 3 (12) DOI: 10.1371/journal.pone.0003868.

2Connor, R., Watson-Capps, J., Sherwin, W., & Krutzen, M. (2010). A new level of complexity in the male alliance networks of Indian Ocean bottlenose dolphins (Tursiops sp.) Biology Letters, 7 (4), 623-626 DOI: 10.1098/rsbl.2010.0852.

Cornered Rat Waves Poisoned Tool, Attacker Flees in Terror!

Screams the tabloid headline…

Is this the plotline for a sequel to The Planet of the Apes in which mistreated lab rats rebel against cruel animal experimenters?

No, it’s actually an accurate (ok, a bit sensationalized) description of the way in which a small African rat has opportunistically found a way to deploy a poison tool (yes, tool, see below) to defend itself from predators.

For years, observers had suspected something was up with the African crested rat (Lophiomys imhausi): it moves sluggishly, acts fearlessly – practically inviting predators to attack it – and twists around to display boldly-patterned black and white bands along its flanks when it’s excited or threated. Some have speculated that these displays could be designed to mimic the appearance of the spiny porcupine or skunk-like zorilla, and over the years there have been reports suggesting that the crested rat may be poisonous, based in part on anecdotes about dogs retreating in fear from the small rodents or showing signs of having been poisoned after crested rat run-ins.

The mystery of the crested rat was cleared up last week, when a team of researchers led by Jonathan Kingdon of the University of Oxford’s Department of Zoology, published their findings about the rat’s unique set of defenses online in the Proceedings of the Royal Society B1.

Poisonous Defense

The researchers found that the crested rat gnaws and chews the roots and bark of local Acokanthera schimperi trees, which contain a substance called ouabain that is used in a traditional African arrow poison known to be capable of killing elephants by amplifying heart contractions. In chewing on the bark and roots, the rat creates a thick gel-like mixture of saliva and plant toxins, which it proceeds to slather onto the distinctively colored fur along its flanks. Here’s a video of the crested rat in which it briefly displays some grooming behavior:

As it turns out, the hairs of the fur in crested rat’s flank-area are highly specialized and extremely well-suited to deliver this self-applied poisonous mixture. These hairs are essentially perforated cylinders containing fiber-like strands that act as wicks, rapidly absorbing the slobbery, poisonous gel and drawing it up by capillary action. When the researchers chemically analyzed the hairs by infrared spectroscopy, they found strong evidence that that they were indeed absorbing and wicking up ouabain from the saliva mixture. Here’s another video of the hairs doing showing off their wicking abilities (that’s red dye in the video, not blood!):

Properly armed with this potent poison and benefited by some additional physical adaptations (an armored skull, enlarged vertebrae, and dense and thick skin), the crested rat enjoys a suite of defenses that allow it to stare down many a predator. The research paper describes the crested rat’s behavior when threatened:

Flaring of the fur is triggered by external interference or attack on the animal, whereupon white and black banding of the longer hairs on either side of the lateral line effects outlines of the tract in a bold white and black ‘target’ design. An aggravated rat pulls its head back into its shoulders and turns its flared tract towards its adversary as if actively soliciting an attack. This display may or may not be accompanied by vocalizations.

No, you don’t want to mess with Lophiomys imhausi.

The researchers characterize the crested rat’s poisonous defense as “toxicity by acquisition” never before reported for a placental mammal, noting that the closest mammalian analogy may be European hedgehogs, who are known to slather their spines with a mixture of toad venom and saliva, presumably to increase the pain and discomfort that their spines can inflict. By contrast, they point out that there’s no evidence that the crested rat needs to create any kind of a wound; rather, the would-be predator is poisoned when it bites – or even just mouths – the crested rat.

So, is the crested rat just a fascinatingly well-adapted defender, or is it a full-fledged tool user?

Tool Use

Tool user! (We at AnimalWise are never shy about making pronouncements … or speaking about ourselves in the “royal we.”)

Even poisonous rats like carrots! (photo credit: Susan Rouse)

Although not mentioned in the research report, the crested rat’s deployment of the plant toxins does indeed qualify as “tool use” as defined in Benjamin Beck’s Animal Tool Behavior, the most complete catalog of tool use in animals. The original 1980 version contained what remains one of the most widely-accepted scientific definitions of the term:

[T]he external employment of an unattached environmental object to alter more efficiently the form, position, or condition of another object, another organism, or the user itself, when the user holds or carries the tool during or just prior to use and is responsible for the proper and effective orientation of the tool.2

In 2011, this treatise was substantially revised and updated, and now contains the following definition:

The external employment of an unattached or manipulable attached environmental object to alter more efficiently the form, position, or condition of another object, another organism, or the user itself, when the user holds and directly manipulates the tool during or prior to use and is responsible for the proper and effective orientation of the tool.3

While it’s not all that much fun wading through the definitions (would they read better in verse?), the authors themselves make it clear that they would consider the crested rat’s “self-anointment” behavior to be tool use: the bark/roots are “unattached environmental objects,” the crested rat uses them to provide itself with a more efficient defensive position, it holds (carries) and manipulates the tool, and is responsible for properly and effectively orienting it.

In fact, the authors have come up with what they call modes of tool use, including several – Affix (attaching an object to the body with adhesive), Apply (attaching a fluid or object to the body without adhesive) and Drape (placing an object on the body temporarily) – which are directly applicable here.4

Moreover, considering only rodents (there are other examples elsewhere in the animal kingdom), the authors specifically call out a number of additional examples of “Affix, Apply, Drape” tool use by self-anointers: rice-field rats that apply the anal gland secretions of the weasel, one of their predators, presumably for concealment purposes; and California ground squirrels, rock squirrels, and Siberian chipmunks that anoint themselves with the scent of rattlesnakes by chewing shed snakeskin, applying dirt (substrate) the snake has been contacted with, and/or anointing themselves with snake urine, all most likely for “olfactory camouflage” purposes.5

So, there you have it. The crested rat is bold, it’s brave, it’s poison, and it’s a tool user!

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1Kingdon, J., Agwanda, B., Kinnaird, M., O’Brien, T., Holland, C., Gheysens, T., Boulet-Audet, M., & Vollrath, F. (2011). A poisonous surprise under the coat of the African crested rat Proceedings of the Royal Society B: Biological Sciences DOI: 10.1098/rspb.2011.1169.

2Beck, B.B. 1980. Animal tool behavior. New York: Garland (as quoted in Shumaker, Robert W.; Walkup, Kristina R.; Beck, Benjamin B.; Burghardt, Gordon M. (2011-04-28). Animal Tool Behavior: The Use and Manufacture of Tools by Animals (Kindle Locations 299-301). JHUP. Kindle Edition).

3Shumaker, Walkup; Beck & Burghardt 2011 (Kindle Locations 372-375).

4Id. (Kindle Location 601).

5Id. (Kindle Locations 1934-1943).

On the Branch of a Tree, Not at the Top of a Ladder

Every so often, it’s good to see something clearly illustrating that it’s not all about us, that evolution doesn’t simply progress its way up a ladder, climbing ever higher until it reaches humans on the top rung.

Genetic comparisons offer one such clear illustration.

For example, now that we’ve fully sequenced the human and chimpanzee genomes, we can take a close look at the different paths our genes have travelled during the six or seven million years since we parted ways from a common ancestor. In that time, humans and chimpanzees have plainly diverged quite a bit — on the one hand, humans have learned to walk on two legs, experienced dramatic growth in brain size, and now excel at speech, language and a whole host of cognitive functions; on the other hand, although chimpanzees are clearly intelligent primates, they still retain many of the physical and behavioral characteristics that they had millions of years ago.

Obviously, then, our genes have undergone the greater process of Darwinian natural selection … right?

Wrong.

The Human-Chimpanzee Genome Comparison

Do you think those humans are ever going to evolve like us? (photo credit: Delphine Bruyere)

A team of researchers led by Margaret Bakewell and Jianzhi Zhang of the University of Michigan1 decided to systematically compare the human and chimpanzee genomes to find out which species’ lineage has undergone more positive Darwinian selection over time. In essence, they lined up the two genomes to identify where they differed, and then used the DNA of the rhesus macaque, which shares an older ancestor with each of us, to figure out whether differences were due to changes in the human or in the chimpanzee DNA.

Moreover, since some DNA changes have no impact on protein production, the team was able to use statistical methods to look at the changes that do impact protein production and identify which of these were positive in the sense that they conferred a survival or reproductive advantage. (Without getting into the mathematical details, genes where a disproportionate number of the DNA changes do impact protein production are the ones where positive selection is taking place.)

In all, the researchers scanned nearly 14,000 genes (greater than 50% of the genes in the primate genome), and carefully controlled for relatively quality differences in the available genomic sequences. Using their most conservative data, they identified 154 genes that were under positive selection in the human lineage and 233 in the chimpanzee lineage. In other words, chimpanzees have 51% more positively-selected genes than humans have.

The research team summed up these findings:

[I]n sharp contrast to common belief, there were more adaptive genetic changes during chimp evolution than during human evolution. Without doubt, we tend to notice and study human-specific phenotypes more than chimp-specific phenotypes, which may have resulted in the prevailing anthropocentric view on human origins.

Interestingly, the types of genes undergoing positive change are not particularly correlated to the areas where we have seen the greatest physical divergence, such as brain size. Rather, as the below charts indicate, the areas of positive selection are widely distributed through biological processes, molecular functions and tissue groups (in the charts, PSG stands for “positively selected gene”) :

What Explains the Greater Positive Selection in Chimps?

The researchers believe that the principal explanation for the findings is that, for most of the time that humans and chimpanzees have evolved separately, the average population size of chimps was 3-5 times as large as that of humans. This is significant, as population genetic theories predict that positive selection is less effective in smaller populations (i.e., in a small group there are simply fewer opportunities for the occurrence of beneficial mutations with survival and/or reproductive advantages).

Now, there are a few caveats to this story. For one, this type of comparison does not necessarily capture recent or ongoing changes that are not yet “fixed” in the genome, so recent positive changes to the human genome may have gone undetected. Also, while this analysis adds up the relative number of genes undergoing positive change, it does not take into account the fact that some changes may be more important than others, as a change to a single gene can sometimes have a dramatic impact. Also, the study focuses on changes to genes that impact the proteins that they produce, but not the way in which those genes are expressed (e.g., whether and when the genes are turned on or off), and gene expression can account for very significant differences between species.

Nevertheless, even with these caveats, this study is an eye-opener.

From a human perspective, we naturally see our distinguishing characteristics as critically important, and often assume that they reflect something special from an evolutionary standpoint. When we look closely, though, we sometimes find that our views are far more subjective than objective. From a broader perspective, we have been just a single species with (for most of our history) a relatively small population, and have accordingly undergone a correspondingly slower rate of natural selection.

Makes one wonder whether the chimps, with all of those positive genetic changes, could have evolved a way for handling debt ceilings and political consensus. Now that would be an adaptation that would come in handy these days!

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1Bakewell, M., Shi, P., & Zhang, J. (2007). More genes underwent positive selection in chimpanzee evolution than in human evolution Proceedings of the National Academy of Sciences, 104 (18), 7489-7494 DOI: 10.1073/pnas.0701705104

Asian Elephant Social Networkers

In a terrific new study in this month’s BMC Ecology1, a team of researchers led by Shermin de Silva of the University of Pennsylvania Biology Department has published the results of extensive, multi-year research regarding the social dynamics of a population of Asian elephants (Elephas maximus) at Uda Walawe National Park in Sri Lanka. The researchers studied 286 adult female elephants from September 2006 to December 2008, observing the social relationships they formed on a one-to-one basis, in small groups, and at the overall population level.

While group social behavior in African savannah elephants (Loxodonta africana) has been studied extensively, this new research is the first detailed, quantitative study of a wild Asian elephant population over such a lengthy time period … and what the researchers found was quite surprising.

You spend all your time social networking! First do your homework, then you can go on Facebook (photo credit: HelpElephants.com)

Prior less comprehensive studies had suggested that Asian elephants form less complex social networks than do African savannah elephants, with Asian elephants forming smaller and looser social groups based primarily on mother/daughter bonds, and rarely if ever involving relationships between unrelated females. In this in-depth longitudinal study, though, a different, more nuanced, portrait of Asian elephant society emerged.

Although, on any given day, the researchers would see only small groups of elephants that didn’t appear to interact extensively, over time, individual elephants formed larger social units that could be remarkably stable across years, even while associations among such units varied quite a bit across seasons.

One-to-One Relationships (Dyads)

The researchers started out by measuring how much time pairs of adult females spent together and found that, at a high level, the frequency of their associations was highly correlated across all five seasons in the National Park (Sri Lanka has a highly seasonal environment, with two separate monsoon seasons, two dry seasons, and a transitional season) – that is, pairs who associated in one season tended to associate in all seasons, and those who did not associate in a given season weren’t likely to associate at all.

Yeah, let's just hang and make nice for now, then we'll hit the rice paddies when nobody's looking! (photo credit: EleAid.com)

In studying one-to-one relationships, the researchers turned their attention to 51 “core” elephants who they thought would provide particularly good data, since these elephants were observed frequently and during all seasons of the year. These elephants formed a total of 478 pair relationships, which the researchers divided out statistically as follows:

  • A total of six (1.3%) of the pairings were “strong” and stable relationships, as measured by the relative percentage of time these pairs spent together during all seasons. Nine of the elephants (17.6%) participated in relationships in this category.
  • A total of 433 (90.6%) of the pairings were “temporary,” with the association peaking during a single season (most of the peaks were in either the transitional or dry seasons). All 51 of the elephants had at least one relationship that fell into this category.
  • A total of 39 (8.2%) of the pairings were “cyclical,” with the associations peaking in frequency during the two dry seasons (interesting, the researchers did not find relationships where the peaks were during the two wet seasons). Thirty two (62.7%) of the elephants had relationships that were cyclical.

Next, the researchers analyzed whether the identities of an elephants’ preferred companions changed over time. Overall, they found that the elephants spent slightly more than 20% of their time with their long-term companions (the top five companions over five seasons) and slightly more than 30% of their short-term companions (the top five for the current season). On an individual level, there was quite a bit of variation: eight (15.7%) of the elephants maintained 4 to 5 of their top five companions for all five seasons, while 16 (31.4%) completely changed their top-five companions during the study.

The researchers cite the example of two elephants, Kamala and Kanthi, who spent nearly all their time together – they were part of the “K” unit (Kamala, Kanthi, Karin, Kavitha and Kalyani, but no Kardashians) that was particularly close – and contrasted this kloseness to an individual named “471” that had few stable companions. (I wonder if this was due to distress over only receiving a number for a name.)

Additionally, the researchers noticed that the elephants who had the most relationships tended to form weaker bonds with each individual partner, whereas those with relatively few pairings tended to spend a relatively large amount of time with each of their companions.

Hmm, these elephants are beginning to sound quite a bit like people…

Small Group Associations (Ego Networks)

At the next level up, the researchers studied so-called “ego networks,” social networks consisting of an elephant and all of the other individual elephants with whom she associated at least once. The researchers focused on 88 of the adult females who they observed in every season, and calculated five measurements for each: (1) the number of her direct companions, (2) the number of ties between the direct companions, (3) the total number of potential ties between each of these direct companions, (4) the ratio of actual to potential ties, and (5) the number of individuals within two degrees of separation of the subject (number of friends plus number of “friends of friends”).

(Note that, assuming at least one of the researchers is within five degrees of separation of Kevin Bacon, this would mean that the entire ego network would be within seven degrees of separation of Kevin Bacon.)

Without getting into the full statistical analysis, the researchers’ principal conclusion was that:

[W]hile a subject’s direct companions do change over time, she has a few that are almost always present; even those that are not present continuously may have been companions in previous seasons. Thus, individuals maintain long-term relationships with others even though they may be apart for one or several seasons and [the amount of time spent together is small].

In other words, the elephants remember their friends and reestablish their relationships even after having been apart for long periods.

Population Level

Finally, the researchers looked at the social structure of the entire population. They found that the elephants in the overall popular had an extensive and well-connected social network, and that the distinct social units within the population were two to three times larger than had previously been seen in the field. Moreover, they observed that many of the social units maintained their integrity across seasons, even as individuals switched units and the connections between the units changed.

For those of you who like to look at dot patterns, below is a colorful series of diagrams depicting the connections between elephants, measured at different societal levels and during different seasons (T1 is the transitional season, D1 and D2 are the dry seasons, and W1 and W2 are, you guessed it, the wet seasons):

Figure 5 from Research Paper

Recap

While the strength of the associations among these Asian elephants (as measured by percentage of time that individuals spent together) is generally a good bit lower than that of the associations among African savannah elephants, most of these elephants had a few strong ties as well as consistent ties that they maintained over several seasons. Further, the Asian elephants were hardly asocial – while their mix of companions did fluctuate over time, they often returned to a subset of preferred companions.

Moreover, through their years of observation and statistical analysis of the elephants at the population level, the researchers found that the elephants’ social units were much larger than had been observed in prior studies, and that these social units were more stable across the years than were the companions of individual elephants.

The researchers speculated that one reason for the surprising findings is that the elephants stay in touch in ways that are hard for humans to detect, allowing the elephants to maintain bonds and relationships that we fail to observe. For example, elephants can communicate acoustically over great distances, and often use scent to follow one another’s paths at night (and, for that matter, even when the other elephants would be in plain sight, at least from the human perspective).

Finally, the researchers are planning to perform a detailed genetic study of the population in order to analyze the degree to which relatedness impacts the social organization of Asian elephant society. We’ll be waiting!

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1de Silva, S., Ranjeewa, A., & Kryazhimskiy, S. (2011). The dynamics of social networks among female Asian elephants BMC Ecology, 11 (1) DOI: 10.1186/1472-6785-11-17.

Sheep: Barnyard Brainiacs

It turns out that sheep are far more intelligent than their reputation for barnyard slowness would lead one to believe. In recent research published in PLoS ONE1, Professor Jenny Morton of the Department of Pharmacology at the University of Cambridge and her colleague Laura Avanzo reported that domestic sheep can perform extremely well on tests of designed to measure cognitive abilities, possibly as well as any animal other than primates.

Professor Morton, who had been studying Huntington’s disease, wanted to find out whether transgenic sheep with a specific genetic defect might be useful in preclinical research regarding potential treatments for this neurodegenerative disease. Because Huntington’s is characterized by cognitive deterioration, Morton was particularly interested in seeing how well sheep would perform cognitively, since suitable research subjects for neurologic disorders like Huntington’s inevitably must undergo systematic cognitive testing relevant to the disease.

Accordingly, Morton and Avanzo devised a series of tests that they gave to seven female Welsh Mountain sheep, six of whom completed the whole study. No word on why all of the ungulate volunteers were female, although my guess is that the males were off rollicking around with male bottlenose dolphins who were avoiding sponge fishing duty.

Welsh Mountain ewe: wool-giver and five-time Jeopardy champion (photo credit: Vertigogen)

The Tests

The tests were designed to measure the ability of the sheep to perform in three areas (discrimination learning, reversal learning and “attentional set-shifting”), which are relevant to what the researchers refer to as executive function – that is, the “ability to learn associations between stimuli, actions and outcomes, and to then adapt ongoing behavior to changes in the environment.” While the sheep took a large number of very specific tests, the tests fell into the following general categories:

  1. Simple discrimination tests. Sheep must choose between two feed buckets that are identical except one is blue the other is yellow. One color contains a food reward; the other is empty. Later “retention tests” repeat the original tests after time has passed to see how well the sheep remember.
  2. Simple discrimination reversal tests. Sheep must relearn the correct answer after sneaky researchers reverse the color of the bucket containing the food reward. (Note: we encountered this type of testing in the earlier AnimalWise post about the clever Anole lizards). Again, later “retention tests are given.
  3. Compound discrimination tests. The rewarded color is the same as in 1 above, but the relevantly-colored objects are now “perforated sports cones” rather than buckets. Additional buckets of irrelevant colors (one black, one green) are placed next to the sports cones, with the food reward in whichever bucket happens to be next to the correctly-colored sports cone.
  4. Intradimensional shift tests. Now, the sheep are presented with new shapes (rhomboids and cones) and new colors (purple and green). The sheep must still make a correct choice based on color, but need to learn the new color to apply.
  5. Intradimensional shift reversal tests. Same as 4, but sheep must relearn correct answer after the researchers change the rewarded color.
  6. Extradimensional shift tests. Again, the sheep are presented purple or green cones or rhomboids, but this time they must figure out now that the reward is based on choosing the correct shape, rather than a particular color.
  7. Extradimensional shift reversal test. Same as 6, but sheep must relearn after researchers swap which shape is rewarded.

Of the above tests, 1 & 3 measure “discrimination learning”; 2, 5 & 7 measure “reversal learning”; and 4 & 6 measure “attentional set-shifting.”

The Results

In a nutshell, the sheep did amazingly well.

They very quickly learned to pass the initial simple discrimination test (within seven sets of eight discriminations). When presented with the first reversal test, their performance initially dropped off, but they learned the new correct answer within three days of testing (11 sets of discriminations). For the compound discrimination testing, their performance again dropped slightly at the outset, but within two days they had this new puzzle figured out as well. Moreover, the retention tests showed that the sheep were able to remember the correct answer after time had passed (six weeks in the case of the simple discrimination test; two weeks for the simple reversal test).

At first, the sheep performed no better than chance on the more difficult intradimensional shift test, but they soon were performing at over 90% correct. They also experienced a large drop off in performance on the extradimensional shift test, but improved gradually until they reached 80% correct on the fourth day of testing. The sheep learned also were able to learn the reversals (within eight sets of discriminations for the intradimensional reversal and within 10 sets for the extradimensional reversal).

Morton and Avanzo summarized the results as follows:

We show that not only can normal can sheep perform discrimination reversal learning tasks, but they can also perform attentional set shifting tasks that test executive function. To our knowledge, this is the first time that these executive functions have been demonstrated in any large animal, apart from primates.

They were surprised by this success, conceding that they hadn’t been expecting the sheep to do well on the more difficult tests and indicating that they were “driven more by curiosity than expectation” in even giving the tests to them.

So, given these results, sheep seem to have gotten a bum rap for intelligence. There are relatively few studies on ovine intelligence, although research has shown that they can learn and remember how to navigate complex maze2 and that they are very good at remembering faces3.  And then there’s my favorite, that they’ve learned to roll their way across hoof-proof metal cattle grids in order to raid villagers’ valley gardens4!

One reason for the mistaken impression about sheep cognition may be that we have a bit of a blind spot when it comes to intelligence. We expect it in ourselves and a few other select animals, but even scientists can be quite surprised when it pops up elsewhere. Perhaps the main lesson here is that we should do our best to remain open to finding intelligence in unexpected places – if nothing else, this sort of a mental stretch will be a good test of our own cognitive abilities.

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1Morton, A., & Avanzo, L. (2011). Executive Decision-Making in the Domestic Sheep PLoS ONE, 6 (1) DOI: 10.1371/journal.pone.0015752.

2LEE, C., COLEGATE, S., & FISHER, A. (2006). Development of a maze test and its application to assess spatial learning and memory in Merino sheep Applied Animal Behaviour Science, 96 (1-2), 43-51 DOI: 10.1016/j.applanim.2005.06.001.

3Kendrick, K., da Costa, A., Leigh, A., Hinton, M., & Peirce, J. (2007). Sheep don’t forget a face Nature, 447 (7142), 346-346 DOI: 10.1038/nature05882.

4See, e.g., BBC News, “Crafty sheep conquer cattle grids,” July 30, 2004.

Female Dolphins Sponge Their Way to Success

After 27 years, scientists finally appear to have unraveled most of the mystery surrounding a very enterprising group of (primarily) female bottlenose dolphins (tursiops aduncus) who live in Shark Bay, off the coast of Western Australia.

Why are those dolphins looking at me like that? (photo credit: Eric Patterson, Shark Bay Dolphin Project)

The story opens in 1984, when observers first noticed that some of the Shark Bay dolphins were breaking off conical marine basket sponges and wearing them over their beaks (rostra). Because only a small percentage of the dolphins in the area engaged in this behavior and it was very difficult to see what they were doing with the sponges, especially when they were underwater, the first research on this behavior wasn’t published until over a decade later.

Preliminary Findings: Tool Use by a Few Females

In a 1997 article in Ethology1, a team of researchers led by Janet Mann of Georgetown University described their initial findings: five female dolphins were regularly seen with sponges, and four additional dolphins (only one of which was a male) were each seen carrying sponges on a single occasion. The regular sponge users were relatively solitary, tended to use the sponges in a deep water channel area, and did not participate in the group feeding and social aggregations to which other dolphins in the group were attracted.

The researchers weren’t sure what the dolphins were doing with the sponges, but they assumed that there had to be some sort of functional advantage, since the sponges were often quite large, covering a large portion of the dolphin’s face, interfering with normal use of the mouth, contributing to hydrodynamic drag, and potentially impacting the ability to engage in echolocation. They considered three possibilities: that the dolphins were playing with the sponges, that the sponges contained some medicinal or other useful compound, or that the dolphins were using the sponges as a tool to aid in foraging.

They concluded that it wasn’t likely that the sponges were being used as toys, as the spongers were relatively solitary, used the sponges methodically for hours at a time, year after year, and didn’t engage in typical play postures, splashing or vocalizations as they carried the sponges. Similarly, they determined that medicinal or similar uses were unlikely, since, among other things, the regular sponge users all seemed healthy and there were no indications that they were ingesting the sponges (although the researchers conceded that this could be difficult to observe).

Hi ho, hi ho, it's off to sponge I go! (photo credit: Eric Patterson, Shark Bay Dolphin Project)

On the other hand, it did seem likely that the dolphins were using the sponges to help them forage for prey: they were seen eating fish when engaging in sponging behavior; they invested an amount of time in carrying sponges similar to that invested by other foraging dolphins; and they made sounds and generally behaved in ways consistent with foraging. The researchers speculated that sponges might be used to protect the dolphin’s face, either from spines or stingers of prey animals or from the abrasive sea floor as they flushed out burrowing prey. In either case, they believed that this would constitute “tool use,” something that had been reported in captive dolphins but never before in the wild.

Finally, the researchers drew no conclusions on why males didn’t engage in sponging, except to note that perhaps it required a degree of solitary living that was at odds with their need to form and maintain cohesive and cooperative alliances.

Additional Findings: A Cultural Tradition of Tool Use among a Related Group of Females

Next, in 2005, Mann’s researcher team expanded on its findings in a paper published in the Proceedings of the National Academy of Sciences2, with salient points of the research including the following:

  • Sponges Are Foraging Tools. By this time, the researchers had found 15 adults in the community who regularly used sponges, only one of whom was a male. Although not a focus of the paper, it appears that the researchers had concluded by this time that the dolphins were indeed using the sponges as tools to protect their rostra as they foraged for prey on the sea floor.
  • “Sponging Eve.” The researchers tested the mitochondrial DNA of the regular spongers and found that sponging had been passed on mainly along a single matriline (line of descent from mother to daughter) and that, due to the high degree of genetic relatedness, all spongers likely descended from one recent “Sponging Eve.”
  • Female Social Culture. After considering in detail whether the sponging behavior could have resulted from either a genetic propensity or some unique aspect of the deep-water channels where the most of the sponging occurred, the researchers found the evidence for these alternatives lacking and concluded that by far the best explanation was that the sponge use was being socially learned and transmitted from mother to daughter. The researchers weren’t overly surprised by this finding, given that studies had already shown that dolphins have uncommonly complex cognitive and imitative skills and the ability to excel at vocal and social learning.
  • Uncommon Cultural Diversity. It was particularly rare to see this sort of cultural phenomenon in a small subset of the overall population (a single maternal line comprising only about 10% of the females in the group). In other studies (for example, involving apes), this type of culturally learned behavior is seen across the entire population.
  • Can’t Explain Males. Once again, the researchers surmised that perhaps males didn’t engage in sponging because they had to associate at high levels with alliance partners, but they left this point open.

The Story Continues: Spongers Are Fit

The story continued to unfold in 2008, when Mann and her team published a paper in PLoS ONE3 that focused in more on whether sponging was an advantageous behavior, or whether the spongers were in some fashion subordinate or less competitive and were making the “best of a bad situation.”

I don't know what you mean, it's no more elaborate than the other hats at the Royal Wedding... (photo credit: Eric Patterson, Shark Bay Dolphin Project)

By this point, recurrent sponging had been seen in 41 of the dolphins and a few more of them were male (29 were females, 6 were males, and 6 were of unknown sex). This still represented a small percentage (about 11% of adult females were spongers) and, although it now appeared that more than one matriline was involved, the data continued to show that the behavior was consistently passed down from mother to daughter, and less frequently from mother to son: there were no instances observed where a calf adopted the behavior if its mother wasn’t a sponger, and of 19 offspring born to sponger females who could be observed and whose sex was known, 91% of the daughters (10 of 11) and 25% of the sons (2 of 8) adopted sponging.

Further, the researchers found that the spongers were highly specialized, not using other hunting techniques and spending approximately 96% of their foraging time using sponges. In fact, the researchers concluded that, due to their lifestyle and specialization, spongers actually used tools more than any non-human animal.

So, was the sponging advantageous or a way of coping for not particularly well-adapted dolphins? Well, the researchers did find that spongers were more solitary and spent more time foraging at deeper depths and on longer dives, but noted that they really didn’t seem to suffer from any kind of fitness cost, as their calving success was equivalent to that of other females in the population.

Since there was no evidence that any kind of competition for food was relegating the spongers to their strategy, the research concluded that sponging simply seemed to be an “all-or-none phenomenon,” that required a specialized approach and a commitment to a single foraging type, but that most likely opened up a particular hunting niche in a diverse environment. While other dolphins could theoretically adopt the strategy, the researchers noted that daughters in particular tend to adopt their mothers’ foraging strategy, and unless the mother was a sponger, a daughter might simply not have had sufficient exposure to develop this highly specialized technique while a calf.

Once again, the team hypothesized about the males, stating: “Male offspring are exposed to sponging as often as female offspring, but do not seem to adopt the behaviour early, if at all. … [M]ales likely range more widely post-weaning, focus on establishing long-term alliances, and cannot afford to adopt foraging tactics that both demand extensive effort and specialization and limit their range and access to females.”

The researchers offered no opinions about whether the male dolphins were simply slow on the uptake or whether they associated sponges with housework to be avoided.

The Latest Chapter: Explaining the Purpose of Sponging

While all of this research had answered many questions and shed light on a fascinating example of tool use in wild female dolphins, one fundamental question remained. Dolphins are great at using echolocation to detect prey (even prey that is buried), so why do the Shark Bay spongers probe the debris-covered sea floor with their noses, risking injury (even with the protection afforded by the sponges) instead of minimizing sea floor contact by simply echolocating for buried prey as they do in other locations (for example, the Bahamas)?

What a mess! This sea floor needs a good sponging! (photo credit: Eric Patterson, Shark Bay Dolphin Project)

This is the question is answered in the latest chapter, a research paper published last week in PLoS ONE4. Mann’s research team had fun with this one, grabbing poles and going sponging themselves. What they found, aside from the fact that dolphins are far more graceful than people, was that the nature of the prey turned up by sponging helps explain the dolphins’ behavior.

It turns out that most of the bottom-dwelling fish that hide in Shark Bay the sea bottom lack swim bladders, gas-filled chambers used by fish to control their buoyancy as they swim up and down. Because they lack the major characteristic that distinguishes their density from sea water, they generate relatively weak acoustic signals and are difficult to detect with echolocation. In addition, the debris (rock, shell and coral) on the sea floor in the area seemed likely to cause “interfering reverberation and echo clutter,” which would further reduce the effectiveness of echolocation.

Moreover, it’s worth it to go after these swim bladderless fish. They are attractive targets, as they are reliably present on the sea floor and exhibit consistent, predictable behavior when rousted out of their hiding places, allowing the dolphins to adopt a single efficient technique as they sponge. Further, bladderless fish tend to have a relatively high fat content, providing hungry dolphins with a particularly energy-rich meal.

So, the sponging female dolphins of Shark Bay really are quite remarkable. They have established a mother-daughter subculture of tool use in the wild, successfully devising a highly specialized way of exploiting an attractive niche in their diverse environment.

You go girl(s)!

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1Smolker, R., Richards, A., Connor, R., Mann, J., & Berggren, P. (2010). Sponge Carrying by Dolphins (Delphinidae, Tursiops sp.): A Foraging Specialization Involving Tool Use? Ethology, 103 (6), 454-465 DOI: 10.1111/j.1439-0310.1997.tb00160.x.

2Krutzen, M. (2005). Cultural transmission of tool use in bottlenose dolphins Proceedings of the National Academy of Sciences, 102 (25), 8939-8943 DOI: 10.1073/pnas.0500232102.

3Mann, J., Sargeant, B., Watson-Capps, J., Gibson, Q., Heithaus, M., Connor, R., & Patterson, E. (2008). Why Do Dolphins Carry Sponges? PLoS ONE, 3 (12) DOI: 10.1371/journal.pone.0003868.

4Patterson, E., & Mann, J. (2011). The Ecological Conditions That Favor Tool Use and Innovation in Wild Bottlenose Dolphins (Tursiops sp.) PLoS ONE, 6 (7) DOI: 10.1371/journal.pone.0022243.

Perchance to Dream…

Do you ever wake up and feel like you’ve spent the whole night replaying a tape of the stresses of the day before? Well, at least you didn’t spend you didn’t spend that day running through mazes. Oh, you did? In that case, you might want to grab a chunk of cheese and sit down for some comfort eating with a friendly rat who can commiserate with you.

Matthew Wilson, an MIT professor of neuroscience, has been studying rats as they work and sleep for years, and has found out that they, too, replay their daily activities as they sleep.

Rat dreaming of running in circles... (MIT image)

In groundbreaking research published in 2001 in the journal Neuron1, Wilson and his colleague Kenway Louie were given an unprecedented glimpse into the dreams of rats by studying rats’ brain activity while they ran through mazes and then later on while they slept. (To clarify, the rats – not the researchers – were the ones who ran through the mazes. Sorry to disappoint you.)

To investigate what happens in the brain during rapid eye movement (REM) sleep, the type of sleep associated with dreaming, the researchers recorded the activity of neurons in the hippocampus (the area of the brain known to be critical to the formation and encoding memories) of four rats, both while the rats ran around circular mazes and then afterwards during REM sleep.

What they found out was striking.

As the rats ran through the mazes, the neurons fired in distinctive patterns that were dependent on where the rats were within the mazes. Then, when the researchers took comparable measurements of the rats’ brain activity later on during the rats’ REM sleep after a hard day of maze running, they found that the rats played back exactly the same neuron activity patterns as had occurred when they originally performed their tasks. More specifically, in 20 of the 45 REM sleep sessions that the researchers measured, they could detect prolonged periods (tens of seconds to several minutes in length) during which the same spatially-correlated hippocampal neurons fired in the same order, with the REM patterns essentially repeating the daytime patterns at approximately the same speed.

During REM sleep, we could literally see these rat brains relive minutes of their previous experience. It was like they were watching a movie of what they had just done.

In his terrific blog The Frontal Cortex2, Jonah Lehrer noted that Wilson was astonished by these results, quoting him as saying, “During REM sleep, we could literally see these rat brains relive minutes of their previous experience. It was like they were watching a movie of what they had just done.”

Wow!

More recently, Wilson and Daoyun Ji, a postdoctoral associate, extended these findings in research published in Nature NeuroScience3. In this newer study, the researchers focused on brain activity during slow-wave sleep (SWS), often referred to as deep sleep, a stage of sleep not characterized by dreaming but thought to be important to long-term memory formation. The researchers wanted to learn more about how the brain consolidates long-term memories during SWS, and whether it replays visual images from daytime experiences as part of the process. To test these matters, the researchers focused on the interaction between two separate areas of the brain: the hippocampus and the visual cortex, which is responsible for processing visual information.

As before, the researchers measured brain activity in four (presumably different!) rats as the rats ran in alternating directions through figure-eight shaped mazes, and then repeated the same measurements while the rats slept both before and after their maze-running sessions. This time, though, the researchers measured activity in both the visual cortex and the hippocampus.

Once again, the findings are notable.

As the rats ran through the mazes, neurons in both brain areas, the visual cortex and the hippocampus, acted similarly, firing in distinctive patterns that were dependent on where the rats were within the mazes. During subsequent SWS periods, the rats replayed these same firing patterns and sequences in both brain areas, much as they had done in the earlier experiment on hippocampus activity during REM sleep. Moreover, at all times, during maze-running activity and later on as the rats replayed their memories during periods of SWS, the brain activity in the visual cortex and the hippocampus were highly correlated.

By linking the visual cortex to this coordinated memory replay process, the researchers were thus able to show that not only were the rats replaying their daytime memories during sleep, but that they were reliving the same sensory experiences, the exact visual images that they had seen during their maze running!

Do these studies provide insight into the neurobiology of sleep, dreams and memory in humans and other animals? All mammals have similar brain structures that seem to operate similarly, and the research was designed to help us gain a better understanding of our own memory formation behavior, but it never hurts to ask these sorts of questions.

Assuming that these findings do have relevance for other species, then it may well be that when your Golden Retriever paddles his feet, rolls his eyes and twitches during sleep, he is indeed reliving that epic battle he recently had with an evil, slobber-covered tennis ball.

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1Louie, K., & Wilson, M. (2001). Temporally Structured Replay of Awake Hippocampal Ensemble Activity during Rapid Eye Movement Sleep Neuron, 29 (1), 145-156 DOI: 10.1016/S0896-6273(01)00186-6.

2The Frontal Cortex, “The Neuroscience of Dreaming,” December 19, 2006.

3Ji D, & Wilson MA (2007). Coordinated memory replay in the visual cortex and hippocampus during sleep. Nature neuroscience, 10 (1), 100-7 PMID: 17173043.

Chimps Don’t Ape Humans – Develop Tools Independently

The more we learn about the capabilities of animals, the less it seems we can claim as uniquely our own. Now it appears that we may even have to share our treasured Flintstones cartoons, as we have learned that we aren’t the only species to have enjoyed an ancient Stone Age history.

Chimp eating nuts and thinking about upcoming Chimpanzee Iron Age

A few years ago, archeologists led by Julio Mercader of the University of Calgary discovered that chimpanzees in West Africa were using stone tools to crack nuts thousands of years ago, before humans had begun engaging in agriculture in the area. The research team, exploring sites located in the Ivory Coast’s Taï National Park, found stone “hammers” that were 4,300 years old and that had all the hallmarks of chimpanzee tools, rather than human ones. Science 2.01 described the tool findings as follows:

The stone hammers that the team discovered, essentially irregularly shaped rocks about the size of cantaloupes – with distinctive patterns of wear – were used to crack the shells of nuts. The research demonstrates conclusively that the artifacts couldn’t have been the result of natural erosion or used by humans. The stones are too large for humans to use easily and they also have the starch residue from several nuts known to be staples in the chimpanzee diet, but not the human diet.

The research team elaborated further in the paper it published in the Proceedings of the National Academy of Sciences2:

This discovery speaks of true prehistoric great ape behavior that predates the onset of agriculture in this part of Africa. The chimpanzee assemblages are contemporaneous with the local Later Stone Age; thus, they represent a parallel “Chimpanzee Stone Age”….

The systematic archaeological study of prehistoric chimpanzee cultures suggests that the “Chimpanzee Stone Age” started at least 4,300 years ago, that nut-cracking behavior in the Taï forest has been transmitted over the course of >200 generations, and that chimpanzee material culture has a long prehistory whose deep roots are only beginning to be uncovered. These findings substantiate the contribution of rainforest archaeology to human evolutionary studies in areas other than the classical savanna-woodlands of East and Southern Africa and add support to fossil discoveries from these other regions indicative of an ancient chimpanzee past.

I love it: the Chimpanzee Stone Age! Also, it’s amazing that this tool use tradition has been passed down over 200 generations, and is still in use today.  Here’s a nice BBC video clip that shows today’s generation of chimps using the same sort of tools to expertly crack open nuts.

Archeology3, the official publication of the Archeological Institute of America, haled Mercader’s research as one of the “Top 10 Discoveries” of 2007, noting that:

The discovery shows that stone tool use is not a behavior that chimpanzees learned recently by watching the farmers who live in the area, as some skeptics believe. Mercader thinks that humans and chimpanzees may have inherited stone tool use from an ancestral species of ape that lived as long as 14 million years ago.

At this point, Mercader’s views on the origins of tool use are still open to debate and further research. The fact, though, that there can even be such a discussion about tool use, a capability once thought to so uniquely identify the human species, illuminates how much thinking we have had to do recently about the common characteristics we share with other animals. Interesting stuff.

We’ll keep you posted as the story unfolds, and let you know as soon as they discover the first prehistoric chimpanzee satellite TV dishes and computer operating systems.

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1Science 2.0, “Hammer Using Chimps Make Us Wonder Where They Learned It,” February 13, 2007.

2Mercader, J., Barton, H., Gillespie, J., Harris, J., Kuhn, S., Tyler, R., & Boesch, C. (2007). 4,300-Year-old chimpanzee sites and the origins of percussive stone technology Proceedings of the National Academy of Sciences, 104 (9), 3043-3048 DOI: 10.1073/pnas.0607909104.

3Archeology, “Ancient Chimpanzee Tool Use,” Volume 61, Number 1, January/February 2008.

Does Berlitz Offer a Course in Prairie Dog?

Yes, that’s right – before your next trip to Arizona you may need to learn another language if you really want to be able to communicate with the natives.

Prairie dog about to raise its hand in English class (photo credit: Northern Arizona University/Con Slobodchikoff)

Professor Con Slobodchikoff of Northern Arizona University has been studying Gunnison’s prairie dogs for the last three decades, and, as reported by BBC News1, believes that these social rodents have some very special language abilities. Slobodchikoff told the BBC:

Prairie dogs have the most complex natural language that has been decoded so far. They have words for different predators, they have descriptive words for describing the individual features of different predators, so it’s a pretty complex language that has a lot of elements.

According to the BBC article:

The researchers found that the prairie dogs are confronted by so many predators that they have evolved different “words” to describe them all.

These words are barks and sounds that contain different numbers of rhythmic chirps and frequency modulations.

Individual prairie dogs have different tonal qualities, just as human voices differ, but different rodents use the same words to describe the same predators, allowing the alarm call to be understood by the rest of the colony.

For example, a single bark may be attuned to say “tall, skinny coyote in distance, moving rapidly towards colony”.

National Public Radio (NPR)2 recently featured Slobodchikoff’s prairie dog research as well, providing additional color about how Slobodchikoff and his students hid near prairie dog villages, used microphones to record shrill prairie dog predator warning cries (“It sounds kind of like ‘chee chee chee chee,’ “ says Slobodchikoff), and then analyzed the sounds using computer programs to parse out the differing frequencies and overtone layers of the prairie dogs’ warnings made in response to humans, dogs, coyotes, hawks and other perceived threats.

The NPR article describes how, after Slobodchikoff noticed that there were variations in the calls used to identify individual humans, he decided to perform further tests to see how specific the prairie dogs were being in describing what they saw:

He had four (human) volunteers walk through a prairie dog village, and he dressed all the humans exactly the same — except for their shirts. Each volunteer walked through the community four times: once in a blue shirt, once in a yellow, once in green and once in gray.

He found, to his delight, that the calls broke down into groups based on the color of the volunteer’s shirt. “I was astounded,” says Slobodchikoff. But what astounded him even more, was that further analysis revealed that the calls also clustered based on other characteristics, like the height of the human. “Essentially they were saying, ‘Here comes the tall human in the blue,’ versus, ‘Here comes the short human in the yellow,’ “says Slobodchikoff.

Amazingly, it doesn’t stop there. Slobodchikoff’s next move was to see if prairie dogs could differentiate between abstract shapes. So he and his students built two wooden towers on each side of a prairie dog village. They then made cardboard cutouts of circles, squares and triangles and ran them out along a wire strung between the two towers, so the shapes sort of floated through the village about three feet from the ground. And the prairie dogs, Slobodchikoff found, were able to tell the difference between the triangle and the circle, but, alas, they made no mention of the difference between the square and the circle.

Prairie dog warning system: "One if by land, two if by sea" (photo credit: U.S. Fish & Wildlife Service)

As the BBC puts it, if Slobodchikoff’s conclusions are correct, it would mean that “the chattering rodents communicate in a more complex way than even monkeys or dolphins.”

Pretty impressive stuff.

What do you think, does prairie dog communication amount to speaking a “language”? Is human language unique in some fundamental sense, or is there a continuum between what the prairie dogs are telling each other and what we talk about among ourselves?

We will have future posts regarding animal communication and linguistic abilities, and further explore the nature of language.  Until next time, chee chee chee chee, and to all a good night!

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1BBC News, “Burrowing US prairie dogs use complex language,” February 2, 2010.

2NPR, “New Language Discovered: Prairiedogese,” January 20, 2011.

Spotted Hyenas: Clever Carnivores, Not Simply Comedians

Underestimated by many, spotted hyenas (Crocuta crocuta) are providing insight into the roots of human intelligence.

Far from being clownish buffoons, spotted hyenas – also known as laughing hyenas – live in large, complex matriarchal communities, or clans, in which social intelligence is critical. They are fascinating animals – although they look something like dogs, they are more closely related to cats, and closer still to mongooses and civets. Female spotted hyenas are the true clan leaders: they are larger and more aggressive than males, socially dominant, and have even evolved to have male-like external features, including a pseudopenis that is extremely similar in appearance to the male’s sexual organ.

Spotted hyenas enjoying the water (photo credit: K. Holekamp)

Kay Holekamp, a professor of zoology at Michigan State University, has been studying these gregarious carnivores for many years, and is particularly focused on how they can help us gain a better understanding of why certain animals, including humans and other primates, have developed high intelligence and large brains (which, from a metabolic standpoint, are extremely expensive to maintain). More specifically, she has been looking at spotted hyena society as a means of probing the “social complexity” theory of intelligence, which posits that brainpower provides a significant edge to animals living in complex social groups, where individuals need to be able to anticipate, respond to and manipulate the social behavior of other group members.

The majority of intelligence research in this area has been performed on primates, but Holekamp notes in recent research1 that social complexity theory predicts that “if indeed the large brains and great intelligence found in primates evolved in response to selection pressures associated with life in complex societies, then cognitive abilities and nervous systems with primate-like attributes should have evolved convergently in non-primate mammals living in large, elaborate societies in which individual fitness is strongly influenced by social dexterity.”

In this research, Holekamp acknowledges that much remains to be learned about social cognition in spotted hyenas, but concludes:

Work to date on spotted hyenas has shown that they live in social groups just as large and complex as those of cercopithecine primates [AW: a subfamily of Old World monkeys], that they experience an extended early period of intensive learning about their social worlds like primates, that the demand for social dexterity during competitive and cooperative interactions is no less intense than it is in primates, and that hyenas appear to be capable of many of the same feats of social recognition and cognition as are primates.

While the paper includes much more detail, the following are among Holekamp’s observations regarding spotted hyena social knowledge and skills:

  • Individual recognition. Spotted hyenas possess a rich repertoire of visual, acoustic and olfactory signals, which other hyenas can use to discriminate clan members from alien hyenas, to recognize the other members of their social units as individuals and to obtain information about signalers’ affect and current circumstances.
  • Kin recognition.Hyenas can distinguish vocalizations of kin from those of non-kin, with intensity of responses increasing with degree of relatedness between vocalizing and listening animals, and kin recognition potentially occurring among hyenas as distantly related as great-aunts and cousins.

    Basking spotted hyena cub (photo credit: K. Holekamp)

  • Imitation and behavior coordination. Although hyenas have not been observed to engage in true imitation (that is, replicating a novel act performed by a species member) the way some primates do, they do appear to modify their behavior after observing goal-directed behavior of other hyenas. In addition, they engage in cooperative hunting involving complex coordination and division of labor among hunters. This cooperation, which enables them to capture prey many times their size, involves – at a minimum – communicating by simple rules of thumb (e.g., “move as necessary to keep the prey between you and another hunter”), if not the operation of higher mental processes.
  • Social rank and social memory. Spotted hyenas are intensely aware of social rank, and they learn quickly where they and their relatives fit into their clan’s dominance hierarchy. They are able to remember previous interactions they have had with other individuals, and appear to remember the identities and ranks of their clan mates throughout their lives. They apply their knowledge of social ranks in many ways, including to avoid conflict, figure out feeding priority, help them choose appropriate mates, determine which social relationships are desirable to establish and maintain, and when to reconcile after conflicts have occurred.
  • Flexible problem-solving. Similar to certain primates, it appears that spotted hyenas are able to achieve short-term goals through a variety of different tactics. As stated in the Holekamp’s research article, “For example, a hyena can avoid aggression by leaving the aggressor’s subgroup, exhibiting appeasement behavior or distracting the aggressor. A hyena can potentially use greeting ceremonies to reconcile fights, reintroduce itself to conspecifics [AW: members of their own species] from which it has been separated, or increase conspecifics’ arousal levels in preparation for a border patrol or group hunt.”
  • Tactical deception. One sign of social cleverness, which should be familiar to all humans, is tactical deception. It appears that hyenas may share this sophisticated behavior as well, as anecdotal accounts of hyena deception include a low-ranking hyena noticing an unprotected meal but ignoring it until higher-ranking group mates were out of range, and other low-ranking individuals similarly emit alarm vocalizations in what appear to be deceptive attempts to gain access to food.

Finally, here’s a brief video in which Holekamp shows one of the ways she and her colleagues have been assessing the puzzle-solving skills and memories of spotted hyenas:

So, hats off to laughing hyenas: they may sound comical, but they are seriously smart!

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1Holekamp, K., Sakai, S., & Lundrigan, B. (2007). Social intelligence in the spotted hyena (Crocuta crocuta) Philosophical Transactions of the Royal Society B: Biological Sciences, 362 (1480), 523-538 DOI: 10.1098/rstb.2006.1993.

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